Precision of DXA-derived Visceral Adipose Tissue Measures in Children and their associations

Purpose/Aims

To investigate the precision and analysis protocol for VAT, SAT, and VAT/SAT ratio and explore precision covariates in a large prospective sample of children and young adults.

Rationale/Background

Visceral adipose tissue (VAT) has been linked to poor metabolic health, including obesity and metabolic syndrome. Excess VAT can have an early onset during childhood. VAT measured by DXA has been shown to well represent CT and MRI VAT in adults. However, few studies have shown repeatability and quality assurance issues for children.

Methods

These data have been collected as a part of a retrospective analysis of prospectively collected DXA scans acquired as part of two studies, the Bone Mineral Density in Childhood Study (BMDCS) and the Genome-wide Analysis Study (GWAS). The combined sample consisted of 2,514 children (10,787 scans, 1,271 girls) aged from 5 to 21 years. The whole-body DXA scans were acquired on five Hologic systems (Hologic, Inc., Marlborough, MA) of similar models (A and W) with up to eight years of annual follow-up between 2002 and 2009. All scans were analyzed centrally by the authors using one technologist using APEX 3.4 software. A unique and comprehensive quality assurance check was completed for all scans including a review of the acquisition criteria set by ISCD and a review of the automatically placed VAT regions of interest. During processing, regions were either repositioned or eliminated on DXA imaging. Duplicate scans were available on up to 150 children (71 girls) for precision assessment which was used to evaluate test-retest precision, both overall and by age group. Short-term precision estimates were calculated as the root mean square error and percent coefficients of variation (RMSE %CV). VAT codes were broken up into either invalidated scans or incorrectly positioned and subsequently corrected.

Results

Precision for all children in terms of %CV and RMSE (g) was 7.9% (12.8g) and 4.1% (24.7g) for VAT and SAT respectively. See Table 1. In general, the late teen group had the lowest precision error CV% (3.1-9.0) when compared to all other groups, and preteens had the highest %CV range (4.6-11.4). A pair of scans is shown in Figure 1 where the auto analyzer correctly positioned the regions of interest for the first scan but not for the second scan. Seven percent (752 scans) of the total number of scans had to be manually adjusted.

Implications

We conclude that the precision of the VAT regions is dependent on age where the precision for late teens is similar to that of adults. All Hologic DXA whole body scans in children should be manually reviewed for region placement for the most accurate and precise results.